Out LCD board supports 24 bit RGB interface. By default colibri iMX6 has 18 bit RGB interface to our custom board with signals of IPU1_DISP0_DATA18~23 connected but unused. Currently switching to standard 24 bit RGB interface is not possible without hardware modification of custom board. Is it possible to redefine 24 bit color mapping (in device tree or somewhere else) so that we don’t have to modify the custom board? For example, assign bit B6 to pin 136 ( IPU1_DISP0_DATA18) instead of the standard pin 80 (IPU1_DISP0_DATA06), etc.
If I understand you correctly you want a mapping similar to how the Colibri T20/T30 do it. E.g. the most significant bits of blue are on IPU1_DISP0_DATA[0:5] and the two least significant bits are on IPU1_DISP0_DATA[18:19].
The i.MX 6 can not be configured to do what you want. Each colour is mapped to at most one set of adjacent bits. The functionality is described in the reference manual, ‘184.108.40.206.1 Bus Mapping Unit’ or the IPU chapter.